1. Field of the Invention:
This invention relates to a protecting device for a capacitor connected in series with an electric power circuit to improve the power factor thereof.
2. Description of the Prior Art:
It is well known in the art to connect a capacitor in series with an electric power circuit such as, for example, power transmission lines, power distribution lines or bus bars for improvement of the power factor thereof to elevate the power transmission or power distribution efficiency.
When a fault such as a short circuit or a simultaneous multi-phase grounding or the like has occurred in an electric power circuit to cause an abnormally heavy current to flow through the capacitor, the terminal voltage across the capcitor may rise to such an extent as to destroy the capacitor. In order to eliminate this defect, an electric gap discharging device has been connected across the series capacitor to enable it to discharge excess voltage beyond the rated voltage of the capacitor to protect the capacitor from excess terminal voltage.
Since the discharge gap device suffers from the damage and wear of the electrode surfaces thereof caused by excess heating due to the flow of discharge current therethrough, a short circuit switch may be closed in response to the gap discharge cuurrent should be connected across the capacitor terminals. The short circuit switch may be returned to its original open position after a suitable time interval or after the termination of the fault in the power transmission line.
Consequently, the shorter the closing time of the circuit or bypass switch, the lighter the duty of the protecting gap device. That is to say, the capacitor bypass switch has a shorter closing time than that of a conventional circuit breaker. The capacitor bypass switch differs also from the conventional circuit breaker in that gas flow should be limited in case a relatively long period is necessary for bypassing the capacitor.